The pandemic virus SARS-CoV-2 has changed the world in devastating ways, taking hundreds of thousands of lives, and new variants of the virus are continuing to emerge. The race is on to get as many people vaccinated as possible in order to reduce the number of infections and illnesses, which can also limit the chances the virus has to mutate even more. There is concern that the vaccines that are now being used might not be effective enough against some SARS-CoV-2 variants. Boosters are one potential solution to this problem.
Many different research groups are also continuing to work on developing new vaccines. Now, scientists at Duke University have published a new report in Nature about a vaccine they created, which has been shown to protect mice and monkeys from various coronavirus infections, including those caused by SARS-CoV-1 and SARS-CoV-2. This so-called pan-coronavirus vaccine can also protect against similar coronaviruses that originate in bats, which is a proactive form of protection against a virus that may one day emerge to cause another outbreak or pandemic disease.
"We began this work last spring with the understanding that, like all viruses, mutations would occur in the SARS-CoV-2 virus, which causes COVID-19," said senior author Barton F. Haynes, M.D., director of the Duke Human Vaccine Institute (DHVI). "The mRNA vaccines were already under development, so we were looking for ways to sustain their efficacy once those variants appeared.
The coronavirus surface carries a molecule called a spike protein, which binds to receptors on human cells to start an infection. Antibodies that can prevent infection may bind to this spike, so vaccines often are designed to generate those types of antibodies; a portion of the spike protein is used in the vaccine, the immune system identifies that portion and uses it to create defensive antibodies. The vaccine the Duke researchers created uses a nanoparticle that carries a part of the coronavirus spike protein. Since the vaccine has been successful in primates, the researchers are hopeful that it will be useful to people as well.
"This approach not only provided protection against SARS-CoV-2, but the antibodies induced by the vaccine also neutralized variants of concern that originated in the United Kingdom, South Africa, and Brazil," Haynes noted. "And the induced antibodies reacted with quite a large panel of coronaviruses."
The investigators built on previous work that identified an individual that had once been infected with SARS (an illness caused by the virus SARS-CoV-1) and determined that this person carried antibodies that protected them against multiple coronaviruses. That indicated to the team that it would be possible to create pan-coronavirus neutralizing antibodies.
A part of the coronavirus spike protein called the receptor-binding domain helps it enter the body, and it can also be targeted by antibodies. In this work, the researchers found a place in that binding domain that is present on multiple coronaviruses including SARS-CoV-2 and variants, and bat viruses related to SARS. This portion of the binding domain makes it susceptible to cross-neutralizing antibodies, so the researchers created a nanoparticle that contained that portion. The nanoparticle vaccine was also boosted with an adjuvant that stimulates the body's immune response.
"Basically what we've done is take multiple copies of a small part of the coronavirus to make the body's immune system respond to it in a heightened way," Saunders said. "We found that not only did that increase the body's ability to inhibit the virus from causing infection, but it also targets this cross-reactive site of vulnerability on the spike protein more frequently. We think that's why this vaccine is effective against SARS-CoV-1, SARS-CoV-2 and at least four of its common variants, plus additional animal coronaviruses."
The nanoparticle vaccine stopped 100 percent of COVID-19 infections in monkeys. This vaccine also stimulated the release of higher levels of neutralizing antibodies compared to current vaccine options or natural human infection.
"There have been three coronavirus epidemics in the past 20 years, so there is a need to develop effective vaccines that can target these pathogens prior to the next pandemic," Haynes said. "This work represents a platform that could prevent, rapidly temper, or extinguish a pandemic."